Diesel engines, particularly those intended for propelling industrial vehicles, use a fuel obtained from the distillation of oil incorporating a fairly high proportion of paraffin products. At temperatures lower than 0.degree. these products have a tendency to form paraffin crystals at a temperature known as the Trouble Point. Then at a lower temperature, generally at about -7.degree., the concentration and size of the crystals becomes such that filters of normal-sized mesh are blocked, which causes the engine to stop. At temperatures lower than -10.degree. a freezing phenomenon can occur, causing seizure of the valve of the supply pump.
The invention proposes devices for heating the fuel by the transfer of external heat energy, consisting essentially of exchangers using water, electrical resistances, or an oil circuit, or a combination of these means. The invention proposes means enabling the thermal exchange to be improved by a mechanical stirring effect, which in itself already has a fluidizing effect and the thermal transfer of which enables the result obtained to be increased to such an extent that the limit of operation is lowered for example from -7.degree. to -20.degree. for a device having a capacity of 150 W, that is a downward offset of 13.degree., but it is possible to reach temperatures of -40.degree. to -50.degree..